Black tea boosts weight loss by altering gut bacteria

With obesity affecting more than a third of adults in the United States, identifying new weight loss strategies is a key priority for researchers. In a new study, scientists reveal how drinking black tea could be one such strategy.

Researchers say that black tea may be just as effective as green tea for weight loss.

Black tea is one of America's best-loved beverages, accounting for around 80 percent of all tea consumed in the country.

When it comes to the health benefits, however, black tea is often overshadowed by green tea, which many studies have hailed for its ability to boost weight loss.

But the new study indicates that black tea should not be disregarded; it may be just as effective as green tea for losing the pounds - it just works in a different way.

Lead study author Susanne Henning - of the Center for Human Nutrition at the David Geffen School of Medicine at the University of California, Los Angeles (UCLA) - and colleagues recently reported their findings in the European Journal of Nutrition.

Both black tea and green tea contain polyphenols. These are antioxidants that protect cellular structures - such as DNA and cell membranes - against damage from free radicals.

Polyphenols from green tea are small enough to be absorbed into the bloodstream and body tissues, and studies have shown that they can alter the liver's energy metabolism in a way that promotes weight loss.

As Henning explains, "Our new findings suggest that black tea, through a specific mechanism through the gut microbiome, may also contribute to good health and weight loss in humans."

Black tea vs. green tea

The team came to its findings by studying four groups of mice. Each group followed a different diet for a period of 4 weeks: a high-fat, high-sugar diet; a high-fat, high-sugar diet supplemented with green tea extract; a high-fat, high-sugar diet supplemented with black tea extract; and a low-fat, high-sugar diet.

The researchers collected liver tissue samples from the rodents in order to measure fat deposits, and they also collected samples from the large intestine, which enabled them to assess bacterial diversity.

At the end of the 4-week dietary intervention, the researchers found that both the green tea and black tea groups lost weight, and their weights became comparable with the low-fat, high-sugar diet group.

The study also revealed that both tea groups experienced increases in gut bacteria related to lean body mass and decreases in gut bacteria associated with obesity.

'A new reason to drink black tea'

On further investigation, the researchers noticed that black tea and green tea affected the liver metabolism of rodents in different ways.

Henning explains that the smaller green tea molecules are absorbed more easily, meaning they can reach the liver directly to affect energy metabolism.

However, black tea molecules are too large to be absorbed in this way. Instead, they remain in the intestine, where they boost the growth of "friendly" gut bacteria and form metabolites that help to control liver energy metabolism.

It was also found that the black tea group had higher levels of a bacteria called Pseudobutyrivibrio, which they suggest could play a role in the differing effects of green and black tea on energy metabolism.

Overall, they believe that their findings indicate that black tea may be just as beneficial for health as the widely acclaimed green tea.

"The results suggest that both green and black teas are prebiotics, substances that induce the growth of good microorganisms that contribute to a person's well-being."

Susanne Henning

"[...] For black tea lovers, there may be a new reason to keep drinking it," adds senior study author Dr. Zhaoping Li, director of the UCLA Center for Human Nutrition and chief of the UCLA Division of Clinical Nutrition.

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